1. Field of the Invention
The present invention relates to a stereoscopic 3D display device, and more particularly, to a glasses-free autostereoscopic 3D display device.
2. Description of the Related Art
Three-dimensional (3D) display may be briefly defined as “all types of systems for artificially generating a 3D screen.”
A system may include software technologies that produce three-dimensional images and hardware for actually displaying 3D content made by the software technologies. The systems typically include a software component because 3D content produced with a particular software scheme are separately required for each 3D stereoscopic display hardware implementation.
Furthermore, virtual 3D display (hereinafter, referred to as a stereoscopic 3D display device) may be defined as all types of systems for allowing a user to experience depth in planar display hardware by using binocular disparity due to human eyes being separated from each other by about 65 mm in the horizontal direction among various factors for allowing a person to perceive a three-dimensional effect. In other words, human eyes view slightly different images (strictly speaking, left and right spatial information being slightly divided) even when viewing the same object due to binocular disparity, and if those two images are transmitted to the brain through the retina, then the brain fuses two images together in a correct manner to allow us to perceive depth. Using this phenomenon, a stereoscopic 3D display device implements virtual depth through a design of displaying left and right images at the same time on a two-dimensional display device such that they are perceived by a left eye and a right eye, respectively.
In order to display two channel images on a screen in the stereoscopic 3D display device, for example, each channel is outputted by changing each row in one direction (horizontal or vertical) on a screen. In this manner, in the case of a glasses-free type from the viewpoint of hardware structure, when two channel images are outputted at the same time on a display device, the right image is incident on the right eye and the left image is incident on the left eye. Furthermore, in the case of a glasses wearing types, a method is used to hide the right image from the left eye and hide the left image from the right eye using specific glasses suitable to each type.
One factor for allowing a person to perceive stereoscopic and depth effects is binocular disparity due to a distance between two eyes, but also closely related are psychological and memory factors, and therefore, 3D implementation methods are typically divided into a volumetric type, a holographic type, and a stereoscopic type based on the level of three-dimensional image information provided to an observer.
One example of the volumetric type is a method of providing a perspective in a depth direction due to a psychological factor and a suction effect that may be applicable to 3D computer graphics in which perspective projection, overlapping, shadow, luminance, movement, and the like are displayed based on calculations. Another example is the so-called IMAX cinemas in which a large-sized screen having a wide viewing angle is provided to an observer to evoke an optical illusion and create the feeling of being sucked into a space.
The holographic type is known as the most complete 3D implementation technique. Examples include laser beam reproduction holography and white light reproduction holography.
The stereoscopic type is a method of feeling a stereoscopic effect using a binocular physiological factor that uses the human brain's capacity of generating spatial information prior to and subsequent to a display plane where associative images of a plane including parallax information are seen on human left and right eyes being separated from each other by about 65 mm and the brain combines them to perceive a stereoscopic effect, as described above, namely, stereography. The stereoscopic type may be largely divided into a glasses-wearing type and a glasses-free type.
A representative method of the glasses-free type may include a lenticular lens mode and a parallex barrier mode in which a lenticular lens sheet on which cylindrical lenses are vertically arranged is provided at a front side of the image panel.
FIG. 1 is a view for explaining the concept of a typical lenticular lens type stereoscopic 3D display device in which a relationship between rear surface distance (S) and viewing distance (d) is shown.
Furthermore, FIG. 2 is a view illustrating a lenticular lens type stereoscopic 3D display device and a light profile, as an example.
Here, viewing diamonds, light profiles, and view data forming a viewing zone are illustrated in FIG. 2.
Referring to FIGS. 1 and 2, a typical lenticular lens type stereoscopic 3D display device may include an upper and a lower substrate, a liquid crystal panel 10 filled with liquid crystals therebetween, a backlight unit (not shown) located on a rear surface of the liquid crystal panel 10 to irradiate light, and a lenticular lens sheet 20 located on a front surface of the liquid crystal panel 10 to implement a stereoscopic image.
The lenticular lens sheet 20 is formed with a plurality of lenticular lenses 25, an upper surface of which is made of a convex lens shaped material layer on a flat substrate.
The lenticular lens sheet 20 performs the role of dividing left-eye and right-eye images, and diamond shaped viewing diamonds (normal view zone) 30 in which images corresponding to the left-eye and right-eye are formed at an optimal 3D distance (d) from the lenticular lens sheet 20 and are normally incident on the left-eye and right-eye, respectively.
The width of one viewing diamond 30 is the viewer's interocular distance (e) to provide parallax images incident on the viewer's left-eye and right-eye, respectively, as a stereoscopic image.
Here, each viewing diamond 30 is formed with the corresponding sub-pixel view data, namely, image, of the liquid crystal panel 10.
View data denotes an image captured by cameras separated by a reference measure of the interocular distance (e).
In such a typical lenticular lens type stereoscopic 3D display device, the liquid crystal panel 10 and lenticular lens sheet 20 are supported by a mechanical body (not shown), and the liquid crystal panel 10 and lenticular lens sheet 20 are separated by a predetermined distance (rear surface distance; S).
Here, a gap glass 26 is inserted into the typical lenticular lens type stereoscopic 3D display device to constantly maintain the rear surface distance (S).
Since a lenticular lens type stereoscopic 3D display device is implemented in a multi-view mode formed based on an initially designed view map, the viewer may view a 3D image when entering a predetermined view zone.
Here, referring to a light profile measured at an optimal viewing distance (d) with reference to FIG. 2, it is seen that the intensity of light is the highest at the center of the viewing diamond 30 and gradually reduces toward the end of the viewing diamond 30. A difference between the maximum and minimum of the intensity of light may be defined as a luminance difference (LD) (ΔL), and typical lenticular lens type stereoscopic 3D display devices show a large luminance difference, thereby having an effect on their image quality.
An image difference between views perceived due to the user's movement between the viewing diamonds 30 is called image flipping, and the difference is greatest when moving from a normal view to a reversed view or vice versa. Accordingly, an image difference between first view data and last view data increases as the number of views increases, thereby deteriorating the phenomenon of image flipping.
In order to implement a multi-view in the related art, a multi-view image captured by a plurality of cameras may be used as an image source or a 2D or stereo image may be received and converted into a multi-view image for use.
In the case of directly receiving a multi-view image, application is difficult in reality since a lot of cost is incurred for the image production, and the number and structure of views required are different for different stereoscopic 3D display devices and configurations.
Furthermore, in order to convert a 2D or stereo image into a multi-view image for use, a depth map and a multi-view may be generated to carry out view mapping based on them. In this case, it may cause image quality deterioration due to the absence of the amount of information and depth reduction due to inner view generation. Furthermore, a multi-view converter is essentially required, and the size of chip and system increases and the time and cost increases as the number of operations applied to compensate for image quality deterioration increases.